I used 2 way radios in a drypack attached to the student's helmet, but they don't last very long, and you will probably pick up all kinds if chatter from fishermen. (It's quite annoying). When they work properly, it's nice, but in reality that isn't very often. I know another guy who bought the helmet with built in radio, and it went bad almost immediately. Don't spend over 100 bucks on a pair of them is my suggestion.

One of my favorite pieces of 'equipment' is a good hat to keep the sun off, and a pair of sunglasses. (I like the Dakine Indo hat with the flap that covers your neck).

Do NOT let your students wear their expensive sunglasses during the lesson. I had a guy drop his fancy Oakleys or whatever, and he let go of the bar and completely turned around away from the kite to look for them. He even stopped the rest of his lesson to continue the search.

Good luck to ya man, teaching isn't for everyone and it's tough to give up your water time. You'll know soon enough if it's something you want to continue in the future.

On that note, after almost 10 years of teaching I have nearly had enough of it- anyone wanna buy a lesson operation in Florida?

A lot depends on location and distance between the teaching area and base if there is a base.
I always took stuff down in a large yellow dry bag and left a good bit of air in the bag when sealing it. That way it's easy to spot and if the tide does catch it then it simply floats at the waters edge.
If you are a good distance from the base then a mobile phone in a waterproof case and/or VHF radio, consider though that it is frowned upon if you don't use correct proceedure when using a VHF but you won't get into any trouble for saving someones life even if you don't have a short range radio licence. First aid kit is essential, I also included an emergency action plan on an A4 laminated paper so if I were to sustain an injury or have to attend a serious incident then the remaining students would have a guide of what to do, knife and whistle are always good, it's amazing how you can yell until hoarse and the student doesn't take a bit of notice but blow a whistle and everyone looks and stops. A spare bottle of drinking water, multi tool like a Gerber type thing. In cross and cross off winds "cross off only mid to low at my shallow location" I would take my boat down either if there were 4 students to help wheel it on the trailer or when I had the luxury of a quad bike. Can be a bit of a pain with fast tides, A good alternative was a sit on top kayak on wheels, spare kit could be taken down on that too. Lightweight windproof jackets can be good and take up very little room, some people break into a shiver and take relief from a windproof jacket for 5 minutes. The list could be pretty endless and could change for each kind of conditions or locations, you may be miles from base or just 200m from base. Common sense is your best friend.

As mentioned earlier, if you are working large tidal flats then an inflatable raft with an anchor to drag out with you would be good. It will carry all your essentials, (water, first aid, cell phone, food etc) and if someone gets hurt you can put them in it and drag them back to land.

Yeah great except question was about EQUIPMENT not personal qualities and attributes but thanks for your input

I want to travel as light as possible so the raft isn't really suitable - plus the tide comes in fast (stays shallow) so I'd be constantly having to run back and get it.

More is better because the farther away you are, the better prepared you should be. Otherwise, you will be more tempted to make a bad decision because of the inconvenience of going back. Also, getting an injured student to medical attention becomes more problematic.

How about a cart AND a 2 or 3 man inflatable boat/raft. Use the cart when no water, put it in the boat/raft when there's water, anchor the boat with a weight or stake. Perhaps the anchor could be permanent with a buoy ?.